An image forming apparatus of an electrophotographic type in which a photosensitive member is electrically charged by a corona charger. Especially, a product using the corona charger which is called scorotron including a grid electrode for stabilizing a charge potential of the photosensitive member has been known. Here, the grid can be divided into two types depending on a shape of the grid. One is a wire grid in which a wire is stretched in a longitudinal direction of an opening, and the other is an etching grid in which a mesh having many holes in a flat plate is formed by etching. In most of the etching grids, for the purpose of improving charging uniformity, thin lines constituting the mesh are oblique to a discharging wire.
The etching grid has an advantage, compared with the wire grid, such that the opening is covered in a wide area (low opening (aperture) ratio), and therefore the photosensitive member is easily controlled to a target potential (high potential convergence property). On the other hand, in the etching grid, compared with the wire grid, a foreign matter (a toner, an external additive, an electric discharge product or the like) is liable to be deposited on the grid.
On the other hand, in the corona charger, when the electric discharge product (ozone, nitrogen oxide or the like) generated with electric discharge is deposited on the photosensitive member, the electric discharge product takes up moisture in a high-humidity environment and causes image defect which is called image flow. Therefore, a constitution in which with respect to a cleaning member for cleaning a surface of the grid electrode and an opening of the corona charger, the grid electrode is cleaned and the same time the opening is shielded by moving a sheet-like shutter in a longitudinal develop of the opening is described in Japanese Laid-Open Patent Application 2012-063592.
In a constitution in which a brush for cleaning the grid and the shutter are provided, when a commonality between the shutter and a driving source is achieved, the number of driving sources (motors) can be suppressed and therefore the commonality is preferred. On the other hand, after the grid is cleaned by the cleaning brush, the opening cannot be closed by the shutter. For this reason, unless a positional relationship between the shutter and the cleaning brush is taken into consideration, the foreign matter deposits on the shutter.
Especially, in a constitution in which the cleaning brush is caused to enter the etching grid to clean the etching grid, depending on shapes of the cleaning brush and the etching grid, the foreign matter deposits on the shutter. When the foreign matter deposits on the shutter, there is a liability that an agglomeration of the deposited foreign matter drops on the photosensitive member by vibration or the like during movement of the shutter, and therefore the deposition of the foreign matter is not preferred.